
充填裂隙
摘要:
岩体中存在的大量裂隙结构(如断层,节理),这些裂隙的存在对岩体的渗流性质和力学特性会产生重要影响。一般岩块本身的渗透系数很小,但是具有裂隙的岩体渗透系数却很大,这是连通的裂隙构成了良好的透水通道的结果,可以认为是裂隙系统构成了岩体的透水系统。考虑到有无充填物条件下岩体裂隙渗流规律的巨大差异,近年来更多学者开展了在含充填物裂隙渗流方面的试验研究。围绕该问题,本文在详细总结了国内外对裂隙岩石及充填裂隙岩石渗流研究的基础上,对充填石膏砂浆和水泥砂浆两种不同水理性质材料岩样的裂隙渗透规律进行了综合和深入的试验测试并提出一种损伤软化模型。主要研究内容如下:
1)依托中南大学测试中心MTS815.02型试验仪器,针对完整岩样与2种不同充填材料的预置裂隙岩样进行了较为系统的渗流试验研究。设计并制作含充填物的不同贯通率的裂隙岩石试样(Φ50×100),研究其在不同裂隙贯通率及不同围压时的渗透性、强度特性等的变化规律。
2)相同类型裂隙岩样随着围压的增加,均引起轴向应力的显著增加。同时,在相同围压情况下,裂隙岩样随结构面贯通率的加大,其各自的应力峰值强度变化表现出逐渐降低的趋势,但这种由于结构面差异造成变化的幅度远远小于围压变化引起的影响。在充填裂隙岩石的渗透性试验中,虽然裂隙岩样较完整
岩样的峰值强度均有明显下降,但比较两种围压时,可发现高围压情况下的下降幅值普遍较小。由此可见,在充填裂隙岩样中,围压因素的作用远远高于结构面贯通率对强度的影响效果。
3)根据结果计算渗透系数得到:充填裂隙岩样的渗透系数较完整砂岩有显著的提高;由于所选两类充填材料的硬化机理不同,在压力作用下,石膏砂浆充填物质更易发生转移,从而造成渗流通道的堵塞,使得渗透率下降,在相同条件时,石膏砂浆充填的裂隙岩样的渗透系数表现为小于水泥砂浆类充填的裂隙岩样;围压加载过程中的试样内部结构受到压缩变形,使裂隙及渗流通道变小,导致渗透性的降低,因此随着围压的升高,试件的渗透率降低,说明侧围压大小是影响试件渗透性变化幅度的决定性因素之一;在其它条件不变的情况下,随着裂隙贯通率的增加,岩样的渗透系数也随之增大,但裂隙通道受充填物的作用使得渗透系数并未出现明显的倍数规律。
4)对不同试样渗透性试验的破坏形式综合分析,认为渗透压作用下的三轴压缩以剪张性破坏为主,并伴随着沿剪切带的张开裂纹。破坏形式符合格里菲斯破坏准则,在压应力作用下,切向拉应力最强的部位位于与主应力方向夹角30-40°;裂隙的端部,破裂首先在这些部位出现,并伴生多条次生拉张裂隙。在孔隙水压力的作用下,破坏形式由剪切破坏转化为以次生裂隙的拉裂破坏为主。
5)从岩石微元强度和岩石微元破坏服从Weibull分布的角度出发,引进岩石微元强度随机分布变量F,推导出岩石在稳定围压与水压作用下受压破裂的损伤演化方程。在此基础上,重点探讨了基于Weibull
分布的岩石损伤软化模型参数与围压、水压的关系,并结合模型参数对模型的影响规律以及岩石渗透破裂的特点对其参数进行修正计算。从而建立符合实际的岩石损伤软化本构模型,提出计算峰值强度的可行性方法。
关键词:岩石、充填裂隙、渗流试验、损伤软化、本构模型
分类号:
ABSTRACT
There is a huge amount of cracks existing in natural rock mass. And it is great impact on epage properties and mechanical properties of rock mass. The permeability coefficient of the general rock mass is very small, but the ones with fracture is very large becau of the connected cracks form the good permeable passage. It is considered that the fracture system constitutes the permeable system of rock mass. According to the big difference of epage law about joint rock with or without filling conditions, recently, more scholars have carried out in the filling fracture epage with the experimental study. Bad on a study on the epage of joint rock and filling joint rock at home and abroad, the experimental study on permeability of pre-t sandstone with gypsum mortar filling and cement mortar filling is carried on and one damage softening statistical
constitutive model is advanced. The main rearch contents are as follows:
1) Relying on Central South University test center MTS815.02 type test equipment, a systematic epage test is carried out for the complete rock samples and two kinds of pre-t fractured rock samples with different filling materials. After completing the design and production of fillings with different penetration rate of fractured rock samples, the variation law of permeability and strength of different joint persistence and different confining pressure is studied.
2) With the increa in confining pressure, it caus a significant increa in the axial stress of the same type of fractured rock sample. In the ca of the same confining pressure, the trend of the peak stress intensity decreas gradually becau of increasing with the structural plane penetration rate of fractured rock samples. The magnitude of the change due to structural differences is much less than the effect of confining pressure changes. In the permeability test of the fractured rock, although the peak strength of fractured rock samples is obviously decread, it is found that the decrea in the ca of high confining pressure is generally small when comparing two confining pressures. This shows the effect of confining pressure is much higher than that of structural plane penetration in the filling of fractured rock samples.
3) The results of calculating the permeability coefficient: The permeability coefficient of the fractured rock specimen is significantly improved. Becau the hardening mechanism of the two types of filling materials is different, gypsum mortar filling material is more prone to transfer under pressure, it caus clogging of the epage channel so that the permeability decreas. The permeability coefficient of fractured rock samples filled with gypsum mortar is less than that of cement mortar in the same condition. The internal structure of the specimen during compression loading is compresd and deformed, so that the joints and epage channels become smaller and the permeability is reduced. Therefore, as the confining pressure increas, the permeability of the specimen decreas. This indicates that the side confining pressure is one of the decisive factors that affect the variation of the permeability of the specimen. With the increa of fissure penetration rate, the permeability coefficient of rock samples also increas in the ca of other conditions remain unchanged. But the action of the fracture channel by the filling does not make the apparent variation of the permeability coefficient.
4) Through a comprehensive analysis of the failure of different sample permeability test, it is found that the triaxial compression under osmotic pressure is mainly caud by shearing failure and is accompanied by the opening crack along the shear zone. The form of destruction conforms to the Gr
iffith Destruction Criteria. The strongest part of the tangential tensile stress is located at the end of the 30-40 ° fracture in the direction of the principal stress. Rupture first appeared in the parts, and associated with a number of condary tensile fracture. The failure form is transformed from shear failure to a crack caud by cracks in the primary cracks under the action of pore water pressure.
5) From the point of view of rock micro-element strength and rock micro-element failure obey Weibull’s distribution, the random variation of rock micro - intensity F is introduced. And the damage evolution equation of rock under confining pressure and water pressure is deduced. The relationship between rock damage softening model parameters bad on Weibull’s distribution and confining pressure and water pressure is mainly discusd. Combined with the influence of model parameters on the model and the characteristics of rock damage, the study calculates and corrects its parameters. A feasible constitutive model of rock damage softening is established, and a feasible method for calculating peak intensity is propod.
KEY WORDS:Rock, Filling Joints, Seepage Test, Damage Softening, Constitutive Model
第一章绪论
1.1研究背景与意义
随着国民经济的快速发展,大量基础设施(包括交通、能源、工业与民用建筑等)相继立项建设,随之而来的深层地下水资源对该类工程的安全和稳定性的影响也越来越突出。越来越多的工程实践表明,由于工程体在修筑和使用过程中导致的裂隙岩体所处复杂地质环境的产生变化,使得裂隙岩体产生了不适应这种变化的效应,进而不可避免地以不同程度的地质灾害(如岩体失稳、涌水及岩爆等)的形式表现出来。如,1959年12月法国66.5m高的马尔帕塞(Malpast)拱坝在初次蓄水过程中全坝溃决;1963年9月意大利瓦依昂拱坝的库内水位上升到700m高程时,左岸距大坝1.8km处,发生约的大型滑坡;1954年12月5日唐山林西矿四水平奥灰水通过断层突水进入矿井,最大涌水量达;唐山范各庄矿1984年6月2日,发生了世界罕见的矿井大突水,是奥陶系灰岩中地下水沿陷落柱导入矿井,其涌水量达,11个小时一、二水平矿井全淹。
后来许多学者对马尔帕塞大坝的失事原因进行了详细的分析。Bellier[1](Bellier,J.,1976)认为,Malpast大坝坝肩岩体的结构面走向与拱坝推力方向平行,在坝肩岩体中形成高的压应力区,引起坝肩岩体结构面闭合,岩体的渗透系数相对初始值大约减小了100倍,导致岩体渗流受阻,而使得等于水库中全水头的压力作用于该岩体之上,造成大坝坝肩岩体沿下游断层滑移而失稳(图1-1a)。Wittke[2]认为,坝前水位升高,作用于坝面的水压力增大,使大坝坝踵附近岩体受拉,倾向下游的岩体结构面在拉应力作用下被拉裂,形成张裂缝,库区蓄水后,库水沿张开裂缝渗透,由于下游隔水断层封堵了渗透通道,致使张开裂缝中产生等于水库全水头的压力,使坝肩岩体失稳(图1-1b)。
图1-1 马尔帕塞大坝失稳机理
尽管这两种分析马尔帕塞大坝失稳机理不同,但分析结果都认为,马尔帕塞大坝失事是由于岩体的渗透压力作用引起的岩体变形,导致大坝破坏。
意大利瓦依昂大坝上游库区大滑坡,也是由于库水位上升,引起岩体中地下水位抬升,增加了岩体的浮托力而引起的一种渗透变形和破坏。由于该水库两岸岩体渗透性良好,库水位上升迅速引起地下水水位上升,滞后时间短。因而,当库水位上升到700m时,在库岸边坡坡脚处产生极大的扬压力,正应力减小,抵抗滑坡的摩擦阻力减小,而引起滑坡。
在矿区开采过程中,有不少岩体的变形与岩体内地下水渗透压力有关。常存在矿山采动应力、地应力和地下水渗透力相互影响、相互作用的岩体水力学问题。如煤矿井中底鼓突水.就是在开采过程中岩体变形引起岩体渗透性的改变,使岩体内或下部岩体内地下水沿连通的节理裂隙运动,增强了对岩体的渗透压力,引起岩体物理力学性质的变化,而导致矿井突水。地下水渗流以渗透压力作用于岩体,影响岩体中应力场的分布,同时岩体应力场使孔隙、裂隙产生变形,影响岩体的渗透性能,这种相互影响作用称之为渗流—应力耦合,简称流固耦合。流固耦合研究的焦点在于固体介质和流体间的力学耦合基本规律。耦合现象和耦合问题越来越受到许多领域的学者和专家的重视,耦合理论从本世纪50年代国外水库诱发地震分析而萌芽,70年代被正式提出,直至80年代以来得到完善和发展[3]。随着人类工程活动范围的扩展和规模的扩大,对这一理论研究的需求显得尤为紧迫。
人类为了生存和发展而开展的人类工程,无论是水电工程,还是矿井开采工程,都存在人类工程干扰力、岩体地应力和地下水渗透力之间相互影响、相互作用和耦合作用问题。在地质环境内,岩体与地下水的相互作用,影响和改善着地质环境的状态。在人类工程活动中,一方面由于工程的开挖,工程荷载施加于岩体之上,改变岩体内部应力场的分布,从而影响岩体的结构,引起岩体中地下水性质及地下水力学特性的改变;另一方面,由于工程岩体的出现,改变了区域性或局部地下水的补给、径流和排泄条件,形成人工干扰下的地下水渗流场,进而地下水对岩体的力学作用的强度、作用范围以及作用的形式亦发生改变,最终影响裂隙岩体的稳定性。据统计[4],90%以上的岩质边坡破坏与地下水渗透力作用有关;60%矿井事故与地下水作用有关;30%-40%的水电工程大坝失事是由渗流作用引起的。因而,研究人类工程作用力、岩体地应力及地下水渗透力的相互作用关系及耦合关系,是岩体水力学的重要任务,也是一项具有理论研究和实际工程应用前景的重大课题。
1.2国内外研究现状
C. Louis[5]提出了岩石水力学的概念,将地下岩体划分为完整岩石和裂隙2 个部分。完整